Methods have been devised for collecting the naphtha vapour and condensing it; the principal objections to these arrangements are that they interfere with the workman's ability to see his work as it passes over the steam-chest, and do not allow the naphtha itself to pass off so completely, owing to the partial obstruction. The enormous quantities of naphtha which are dissipated in the spreading-rooms of some of the largest establishments, afford sufficient evidence of the want of some suitable means for this object. One plan which has been used, and which certainly does collect some of the naphtha, consists of a rectangular iron hood, of such dimensions as to cover the steam-chest, or the greater part of it, and raised towards the middle, where it opens into a zinc chimney or flue, and passes down, outside the building, into a receiver, kept cool by running water. The vapour is mixed with so much air, which passes away charged with the naphtha vapour, that it is only possible to collect a very small proportion of the latter. Bruce Warren's method has been used with success. Its peculiarity lies in collecting the naphtha vapour by indiarubber, which is capable of abstracting solvent vapours from air charged with them.
The air, loaded with the vapour, is made to traverse a series of trays containing laminated rubber, which Is required either for solution or for dough; or the naphtha may be recovered by distillation, and the rubber be used over again.
Fig. 1 shows an arrangement for spreading and doubling at one operation. B is a roll of fabric, passing under a knife D, in the front of which is placed, along the whole width of C, a roll of dough or cement; E, 2 beams of yarn, warped in the usual manner, pausing through the reed V, and on to the adhesive surface of C. The pressure regulated by H on the rollers A1 A2 A3 firmly unites the whole into one fabric G. Instead of the yarns, a woven fabric or fleece may be employed, as on B. The rollers are hollow, so as to admit steam.
At Moseley's works in Manchester, the escape of the naphtha vapour into the atmosphere of the spreading-room is obviated by covering the steam-chest with a shallow box, in such a way that the vapour rising into the space thus enclosed can, by means of a fan, be drawn off by a pipe that enters it at the farther end. The vapour mixed with air, as drawn from all the machines, is driven into a condensing apparatus connected with the freezing machine in use on the premises for other purposes, and there the naphtha is condensed and recovered. The average saving thus effected amounts to over 70 per.
At Quinn's factory at Ley land, near Preston, the vapour dilated with air, similarly drawn off, is absorbed by means of oil. This method is specially applicable to factories in which a freezing machine is not required for other purposes. The naphtha is recoverable by distillation of its solution in the oil. Figs. 2 and 3 represent a spreader in Quinn's works with its cover a of thin galvanised iron; plates b of glass are introduced to permit the operations to be watched; at the farther end of the spreader a flap c, made of canvas, extends from the end of the cover over the roller d beyond, so as to prevent any escape of naphtha in that situation. From the middle of the cover a 3-in. pipe e rises, and enters a main f with which other similar pipes are connected; g, material entering the spreader; h, rollers conveying the spread fabric to the drum on which it is gathered.
Fig. 4 represents the plant employed at the same works to effect the condensation of the naphtha, and to recover it for future use. The main pipe a from the spreading-room leads to the bottom of a oil; c is a pipe descending from the top of the scrubber to a Baker's blower d. The action of the blower is to draw the mixed air and naphtha vapour from all the spreading - frames through the main pipe and scrubber down the discharge pipe into the open air. In its passage up the scrubber, it meets the oil, and the naphtha is absorbed by it, nothing but air being discharged at the blower. The oil with naphtha in solution runs into a tank or well », from which it is pumped again and again into the scrubber, until it is sufficiently saturated with naphtha. The particular arrangement of the interior of the scrubber adopted here, is that patented by Henry Green of Preston, am! used in the gasworks there for scrubbing; gas. The recovery of the naphtha from the heavy oil is effected in the same way as a similar separation is effected at shale-oil works. The solution is pumped up to a tower f filled with stones, and is made to trickle down, the bottom.
The steam separates the naphtha, and both pass together by the pipe g to the worm condenser A. The remaining parts of the apparatus figured are devoted to the subsequent separation of the condensed naphtha and water, and 'the rectification of the naphtha first by mixing it with sulphuric acid and then by distillation. By the use of this apparatus the amount of naphtha recovered on the average is 46 per cent. of the whole used. It would probably be greater if the spreading were performed more slowly. Drying Spread Fabrics. - After the goods leave the spreading-machines, they are hung up for a few days in a warm room, so as to expel the little naphtha which is retained by the rubber, and which it gives up very slowly.
This drying helps to remove the smell of the naphtha, and prevents blistering in curing. The quality of the solvent used, and the temperature of the drying-room, determine how long this " hanging up " must last before curing. As rubber licks up, as it were, the vapours and odours which float nbout in the drying-room, it would be infinitely better to have a scries of drying-rooms, so as not to hang up the more recently spread goods with those which have more or less completely lost their smell of naphtha. Goods which are cured by the cold process are hung up in the same way; but as they have always a more disagreeable smell, they should have a separate hanging-room to dry in.